For many years it has been recognized that overhead fire sprinkler systems aid in limiting the destructive effect of fires. In the last 20 years the growth and use of sprinkler systems has been dramatic. Thus, while just a few million sprinkler heads per year were being installed in the United States in 1970, the number has increased to approximately 28 million sprinkler heads in 1985, and reportedly 40 million sprinkler heads in 1988.
As a result of the benefits of sprinkler systems, the use of sprinkler heads has grown to the point where they are now mandated in substantially all new commercial buildings.
The basic overhead sprinkler system features a source of water which is distributed through the area to be protected by horizontal supply piping concealed above the ceiling. At intervals along the supply piping, also called run pipe, are short sections of drop pipe to which the sprinkler heads are to be attached. Since the distance between the drop pipe and the desired position of the sprinkler head may vary from location to location, the sprinkler head is commonly attached to the drop pipe by an adjustable pipe connection. This adjustable pipe connection has not changed significantly in the past 20 years and generally consists of an outer pipe section having a threaded opening at one end for screwing onto the drop pipe with an expanded section at the other end having interior threads. A second pipe section having O-rings at the top and threads on its outer surface is then screwed into the outer pipe. By varying the amount of the interior pipe which is screwed into the outer pipe, the length of the connector may be varied. The sprinkler head is then screwed into the lower portion of the inner pipe.
Although the standard type of connection works properly, the close tolerances required for the threading connections between the inner and outer pipe generally require the connector to be assembled off site or for use on site by a skilled worker who must be taken from other jobs for a significant period of time.